Accession No
2467
Brief Description
transit theodolite, by Cooke, Troughton and Simms, English, 1939
Origin
England; York
Maker
Cooke, Troughton and Simms
Class
surveying
Earliest Date
1939
Latest Date
1939
Inscription Date
1939
Material
metal; glass; wood
Dimensions
box length 315mm; breadth 245mm; height 175mm; horizontal circle diameter 101mm; telescope length 160mm; height 240mm
Special Collection
Provenance
Transferred from Department of Engineering, University of Cambridge, Cambridge, England, 09/1979.
Inscription
‘COOKE TROUGHTON & SIMMS Ltd
YORK ENGLAND No 39313’ (on horizontal circle)
‘1939’
Description Notes
Transit theodolite, by Cooke, Troughton and Simms, 1939.
Metal alloy construction with grey finish. Telescope focussed internally by milled ring on end of axis. Inverting, screw focussing eyepiece. Sights on one side and graduated bubble on the other. Second bubble mounted outside frame by brackets attached to the axis; levelled by screw through the frame. Horizontal and vertical circles completely enclosed. Micrometer microscopes attached to the plate by translucent glass tubes which help to illuminate the scale. Microscopes for the horizontal circle are ‘broken’ so that they can be read more easily. All read to 10˝ of arc. Third bubble on the horizontal circle. Clamp and motion screws for vertical circle, horizontal circle and horizontal scale. 3 levelling feet clamped between parallel plates. Plumb-bob. Lens cover. Ray shade. Diagonal lens. Fitted wooden box and case containing spare cross hairs.
Condition
References
Events
Description
The Theodolite is a relatively, simple tool used for measuring angles, both horizontal and vertical. They work using the same principles as a protractor, the ‘point A’ is located and the angle noted, and then the telescope is pointed at ‘point B’ and the second angle is taken.
The telescope on this theodolite can be rotated to sight in either direction without moving the instrument itself. Both horizontal and vertical divided circles are enclosed to exclude dust and are read through microscopes. The adjacent plumb-bob is used when setting-up, to ensure that the theodolite is truly vertical on its tripod.
This instrument was made in 1939 – compare it with the nearby earlier instrument by Troughton & Simms which was made around 1900.
History of the theodolite
Gemma Frisius proposed the idea behind the theodolite in 1533. At the time new methods of surveying were being used and by combining an Alidade, a magnetic compass and the degree scale on the back of an Astrolabe, the calculations made by modern theodolites could be observed. Unfortunately, this method was not practical due to the combination of instruments. The best of the attempts to simplify the process was the ‘theodolitus’, first described in print by Leonard Digges in 1571.
However, this instrument could only take measurements in the horizontal plane. Despite this it was still thought of as the ‘common’ Theodolite up to the late 18th century.
During the 19th century the Altazimuth Theodolite was considered the most useful theodolite, as it could measure on the horizontal and vertical planes. Three notable types of Altazimuth Theodolite were developed: The Everest Theodolite, the Plain Theodolite and the Transit Theodolite. It is the Transit Theodolite, which is still used today.
10/03/2009
Created by: Dr. Anita McConnell on 10/03/2009
FM:42887
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